Methods of charging a secondary battery installed in an electronic device such as a portable terminal, a video camera or the like are divided into two types of charging methods, that is, a contact-type charging method and a non-contact-type (wireless) charging method. The contact-type charging method is a method in which a battery is charged by bringing an electrode of a power transmission device into contact with an electrode of a power reception device.
The contact-type charging method has been generally used in a wide range of applications since a device used in the method has a simple structure. However, as a variety of small-sized and lightweight electronic devices are manufactured to reduce the weight of the electronic devices, poor charging (a charging error) may be caused due to the lack of a contact pressure between the electrode of the power reception device and the electrode of the power transmission device. Also, it is necessary to prevent an increase in temperature of a secondary battery since the secondary battery is vulnerable to heat. Also, attention should be paid to a circuit design to prevent overcharging and over-discharging. To cope with such problems, the non-contact-type (wireless) charging method is now under consideration.
In the case of the non-contact-type (wireless) charging method, a structure in which coupling is reinforced using a planar coil and a magnetic sheet has been proposed to manufacture the small-sized and lightweight electronic devices. However, such a non-contact-type (wireless) charging method has a problem in that heat is generated in the devices due to an eddy current caused by electromagnetic induction. As a result, a large amount of power cannot be transmitted, resulting in a long charging time.
In particular, there is need for development of a magnetic sheet material to solve the above-described problems regarding the heat generation when applied to such a wireless charging method, thereby enhancing thermal conductivity of the magnetic sheet material itself.